*note that the reason you want to buy fish that was frozen prior to your buying it is to avoid parasites. It doesn't work for you to freeze it at your house. The average home freezer doesn't reach low enough temperatures to kill off the nasties that you want to avoid. You can make it hours ahead, but there are some subtle taste changes if you do because the citrus continues to "cook" the fish. That's why I recommend serving it within an hour of the end of your chilling time.